A primary goal in loudspeaker, or simply “speaker,” design has been sound quality. With the advent of mobile media players such as smart phones, iPods®, and other devices, there has been an effort to develop small profile loudspeakers, and in particular wireless loudspeakers that receive a stream of digital information to translate into sound via one or more driver speakers. However, such smaller loudspeakers typically sacrifice sound quality and/or frequency response due to their small size.
Typically, loudspeakers include an enclosure and at least one sound transducer, or active driver speaker having a driver surface or diaphragm that produces sound waves by converting an electrical signal into mechanical motion of the driver diaphragm. An audible sound, or “sound wave”, is produced by periodic pressure changes propagated through a medium, such as air. Sound transducers, such as active driver speakers, typically generate sound waves by physically moving air at various frequencies. That is, an active driver speaker pushes and pulls a diaphragm in order to create periodic increases and decreases in air pressure, thus creating sound. High-frequency sounds have small wavelengths, and thus require only small, fast air pressure changes to be produced for a given perceived loudness. On the other hand, low-frequency sounds have large wavelengths, and accordingly require large, slow air pressure changes for the same perceived loudness. The size of the pressure change is dependent on the amount of air the sound transducer or active driver speaker can move at a desired frequency. In general, a small, lightweight diaphragm is efficient at producing high frequencies because it is small and comparatively lightweight, but may be inefficient at moving sufficient air to produce low frequencies. In contrast, a large diaphragm may be well suited for moving a large amount of air at low frequencies, but not fast enough to produce high frequencies efficiently. Thus, where space is available, many systems employ more two or more active driver speakers of different sizes in order to better achieve a flat frequency response across a wide frequency range.
The diaphragm of an active driver speaker vibrates in two directions, producing a sound wave at one side (front) of the diaphragm that is 180 degrees out of phase with a sound wave produced at the other side (rear). Since identical sound waves 180 degrees out of phase cancel each other, a “baffle” or wall is employed to separate the front and back sound waves to prevent the rear sound wave from canceling the front sound wave. The baffle is incorporated into a box, as (an ideally) infinite-sized baffle is physically impractical. A “sealed box” system removes almost all effects of the rear sound wave. However, unless additional measures are taken, such a “sealed box” system inefficiently permits only half of the sound waves (i.e., the front sound waves) produced by the active driver speaker to be used.
One technique for improving sound quality and taking advantage of the sound waves produced at the rear of an active driver speaker, particularly at low frequencies, is to introduce one or more tuned ports through a wall (usually a front (baffle) or rear face) of the speaker enclosure. The port, also known as a duct or vent in a bass reflex system, is a passive device. That is, it does not receive an electrical signal as would an “active” device such as an active driver speaker. Each tuned port typically includes a cylindrical tube that penetrates the wall of the enclosure at one end and extends into the enclosure at the other end. Such a cylindrical tube has a cross-sectional area and length that together are configured or “tuned” to determine a range of frequencies at which the cylindrical tube may resonate and vent air, generally enhancing the lower frequencies and the overall sound reproduction in general. Much like when a person blows across the opening of a jug, the compression and rarefaction of air in the enclosure due to the active driver speaker's movement produces sound at the tuned port. The tuning of the port addresses the phase differences between the front and back sound waves and thus permits the rear sound wave to be utilized, thus increasing efficiency and enhancing the range of frequencies to which the port(s) are tuned. This permits enhanced response at the lower frequency range and/or permits use of active driver(s) that are less responsive at lower frequency due to size or quality.
However, openings, such as sound ports, in the enclosure are, by definition, holes in the enclosure, and are not sealed or weatherproof because sealing closes and impedes the sound port, thus inhibiting inward and outward airflow from within the speaker enclosure via the sound port and therefore causing distortion. In addition to unsuitability for sealed, weatherproof implementations, use of tuned sound ports limit the size and geometry of an enclosure into which they are placed because the low frequencies to which they are tuned typically require large port length and/or diameter, and thus large enclosures.
Another technique for improving frequency response, and therefore sound quality, in a loudspeaker is to use a different passive device called a passive radiator, or passive diaphragm. Like active drivers, passive radiators typically include a sound radiating surface, or diaphragm, attached via a suspension mechanism to a support structure and/or wall of the speaker enclosure. The radiator surface and suspension mechanism are typically tuned by their mass, flexibility/compliance, and surface area to move in response to compression and rarefaction of air in the enclosure, which results from movement of the active driver(s). Movement of the radiator surface causes movement of air outside the enclosure, which causes sound to be generated at the movement frequency. However, passive radiators are more expensive than sound ports, require more complex configuration due to the method of tuning (typically by adding weight to the radiator surface), and typically require large surface areas (at least two times the surface area of the active driver speakers), thereby requiring a larger enclosure.
Moreover, conventional small-size loudspeaker designs that implement a passive radiator are limited by the surface area of an enclosure and/or by an undesirable radiating direction resulting from a non-ideal placement of the conventional passive radiator. For example, a small-size loudspeaker design may use a necessarily small passive radiator in a front baffle in order to fit between active driver speakers, or may use a rear-directed passive radiator in order to take advantage of additional surface area unimpeded by active driver speakers. These configurations are less than ideal, resulting in a deficiency of sound quality.
So far, there is no wireless loudspeaker that is small and compact, completely enclosed and sealed so to be weatherproof, and providing high sound quality. The devices, systems, and methods disclosed herein are designed to overcome these deficiencies.